Add Flutter app skeleton

app/lib/main.dart

@@ -0,0 +1,9 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import 'src/app.dart';
+
+void main() {
+  WidgetsFlutterBinding.ensureInitialized();
+  runApp(const ProviderScope(child: Tdc114PlusApp()));
+}